A number of saturated fluorocarbon compounds and azeotropes are commonly used as refrigerants in various types of refrigeration systems. These refrigerants have different properties such as boiling points and vapor pressures that dictate to a great extent the refrigerant's suitability for any intended use. Refrigeration systems are generally classified as either high pressure systems or low pressure systems depending on the operational pressure of a particular unit. The refrigerants used in these systems are therefore commonly referred to as either high pressure or low pressure refrigerants depending upon the nature of the system in which they are used.
In many of these refrigeration systems, a small amount of oil is circulated with the refrigerant. Both the refrigerant and oil contained therein, however, tend to absorb and hold water to some degree. As a result any water finding its way into the system is captured within the refrigerant. The presence of excessive moisture within the system can cause ice to form within the system and corrode metal parts through the formation of strong mineral acids, adversely affecting the operation of the unit. Early detection and removal of this unwanted contaminant is necessary in order to maintain the system in efficient operating condition.
Acid is sometimes formed by the refrigerant being chemically broken down due to the system compressor overheating. Like water, those acids have a dew point close to the refrigerant and thus can be cycled through the equipment in the refrigerant flow and build up in the refrigerant to a level where the system is eventually damaged. Contaminant tester tubes have been developed that are arranged to detect the amount of acid and water in a high pressure refrigerant sample.
In high pressure systems, the presence of acids and water is detected by drawing a high pressure sample from the system through the purge valve. The refrigerant sample is typically at a pressure of about 200 psi and is thus thoroughly vaporized. The sample is passed through a flow restriction designed to meter a volume of refrigerant sample. The sample, which is still in the vapor phase is then passed through the tester tube where it reacts with specially prepared chemicals to give a visual indication of the amount of acid and water contained in the sample. Because the sample is drawn from the system in the vapor phase throughout the testing period, any contaminants in the sample are homogenously distributed within the sample. The percentage of a given contaminant in a known amount of sample is thus truly representative of the percentage of the contaminant present in the refrigerant contained within the system.
Attempts to adopt contaminant tester tube for use in testing low pressure systems have, however, heretofore been generally unsuccessful. The low pressure refrigerants generally are those that have normal boiling points at or below room temperature. Under normal operating conditions these refrigerants will exit the system in the form of wet mixture wherein part of refrigerant is in the liquid phase and part in the vapor phase. Accordingly, the distribution of contaminants within the sample is non uniform and thus not representative of the amount of contaminant found in the system. The flow pressures make the sample difficult to handle and the sample flow through the tester tube is unpredictable. A high percentage of liquid in the sample further tends to degrade the sensitivity of the detecting chemicals and thus leads to erroneous sample readings.